The present invention is directed to a drilling device formed of the hollow cylindrical retainer and an annular drill bit detachably engageable with the retainer. These two parts overlap in an axially extending region and at least one projection is provided on one part and at least one recess in the other part for receiving and holding the projection. The recess is formed of an axially extending first section followed by an axially extending second section into which the projections can be inserted. The axially extending sides of the second section extend circumferentially from the corresponding axially extending sides of the first section and the width of such extensions corresponds approximately to the width or circumferential dimension of the projection.
In drilling devices with cutting members in the form of drill bits tipped with diamonds and subject to intense wear, it is known, for economic reasons, to connect the drill bit detachably with the retainer so that it can be replaced. In such a drilling device, as disclosed in DE-GM No. 8 512 878, a bayonet-type connection is used between the retainer and the annular drill bit. This known drilling device has the disadvantage that it is difficult to remove it from a borehole. Since rotation for removing the drill bit, counter to the working rotation direction, results in the projection located on the holder or retainer being aligned in the region of a recess on the drill bit open toward an end of the bit. Restoration of the detached connection between the retainer and drill bit is possible only by rotating the retainer with respect to the drill bit in the working direction. To enable removal of the drill bit by the retainer, the projection must be engaged in the closed region of the recess in the drill bit. Such an arrangement presents difficulties in actual practice.